To operate properly, electrical circuitry often requires a supply of voltage at a negative potential with respect to ground (i.e., a negative voltage). Such is typically the case for a disc drive, which is a digital data storage device which enables a user of a computer system to store and retrieve large amounts of data in a fast and efficient manner.
A typical desktop computer disc drive requires a variety of operational voltage input levels, including negative five volts (-5V) and positive five and twelve volts (+5 and +12V). These voltages can be supplied externally by a computer power supply, or generated internally by appropriate circuitry of the disc drive. For example, some disc drives incorporate an inverting power supply to generate the requisite -5V from an externally supplied +5V input.
In a typical drive, data are magnetically stored using a plurality of read/write heads which controllably access recording surfaces of a plurality of corresponding, rotatable discs. The heads are moved relative to the discs by an actuator assembly and a closed-loop, servo control system. A preamplifier/driver circuit, typically mounted directly to the actuator assembly, facilitates the writing and reading of data by providing write currents to the heads during a write operation and read bias currents to the heads during a read operation.
A typical preamplifier/driver circuit utilizes a negative voltage (such as -5V) in the generation of both read bias and write currents. It is desirable that the negative voltage be provided at a nominally constant level, as noise and voltage fluctuations present in the negative voltage can adversely affect both the writing and reading of data.
A variety of negative voltage supplies have been disclosed in the prior art, including European Patent Application No. 91 120 787.6 (published Jun. 10, 1992 as Publication No. 0 489 412 A2) and International Patent Application No. PCT/US93/12178 (published under the Patent Cooperation Treaty on Jun. 22, 1995 as Publication No. WO 95/17036). These and other similarly constructed prior art negative voltage power supplies typically utilize a capacitor which alternatively stores a charge from a positive voltage source and then transfers the charge to generate the negative voltage across the load.
Although operative for some applications, the increasingly stringent requirements particular to disc drive applications such as faster current responses and significantly lower levels of ripple distortion over a variety of current loads limits the feasibility of such prior art sources. There is a need, therefore, for an improved negative voltage supply capable of outputting a low ripple, fast-response, constant negative voltage over a wide range of loads.